BBC News with Jonathan Izard.

Police say at least two people have been killed and 23 injured in two powerful explosions right by the finishing line of the Boston Marathon. The

blast

s took place within seconds with each other as hundreds of runners were ending the race in the US city cheered on by a large crowd. Paul Adams reports from Washington.

The explosions occurred within seconds of each other close to the finish line on Boylston’s street in the center of Boston. Four hours into the race there were still plenty runners on the street, and the crowds were dense. Television picture showed smoke billowing up from among the flags lining the route. One runner collapsed apparently struck by an object seconds later as terrified onlookers tried to get away. Picture showed another plume of smoke rising from the second blast down the road. Emergency workers immediately began tearing at the pavement barriers and flag poles to get the wounded behind. There were clearly many injured people. Injured spectators were carried to the nearby medical tents set up to look after exhausted runners.

Some news just in. Boston police said the explosions at the finishing line of the city's marathon were almost simultaneous. They say no further explosive devices have been found so far near the finish line, but the investigation is ongoing. The Boston police commissioner Edward Davis told the news conference that there had been a third explosion. "We have, at this point of time, determined that there has been a third